1. Field of the Invention
The present invention relates to the field of technology involving pneumatic-hydraulic driving devices for the knockout mechanism associated with the slide of a press-machine. More particularly, the invention relates to a system for controlling the cushioning and knockout motions to facilitate removal of punched work by a transfer machine.
2. Description of the Prior Art
In conventional pneumatic-hydraulic driving devices, the hydraulic output chamber is constructed to communicate with the knockout cylinder at all times during punching of the work under cushioning. However, this arrangement produces problems which prior art technology has been unable to solve.
Because the piston of the knockout cylinder functions to expand and contract elastically with the hydraulic pressures applied by the device, after the slide of the press-machine crank approaches its bottom dead point, the work is pushed by the pad-frame through the downward force of the knockout cylinder, thus causing the work to be punched under a cushioned condition. Just after punching, when the slide is elevated, the pad-frame continues to push the work, with the latter thereby being knocked out by the pad-frame from the upper die onto the lower die. Heretofore, the knocked out work remains on the lower die, thus causing difficulty in transferring the work out of the press-machine by the chute of a transfer machine. This situation requires additional time to remove the work and in turn increases punching cycle-time, a particular disadvantage under mass-production conditions.